BEN factors are conserved CSL co-repressors in Notch-mediated neural development. Our general goal is to understand how cell signaling pathways mediate accurate transcriptional gene control during development. We focus on the Notch signaling pathway and its roles in directing neural cell fates and states. We strive to elucidate general principles of gene regulation by combining studies in both Drosophila and mammalian model systems. This proposal describes first in vivo functional studies of BEN-solo domain proteins. From our Drosophila work, we found that the BEN-solo factor Insensitive (Insv). regulates Notch signaling and peripheral nervous system development by acting as a direct corepressor for the Notch transcription factor CSL. We will further study its genetic requirements, dissect its functional domains, and elucidate how it cooperates with other chromatin factors to induce transcriptional repression. We build upon this proprietary knowledge to study roles of mammalian BEN-solo factors during neural development, and we have preliminary data on their ability to inhibit Notch signaling and affect neural stem cell self-renewal and differentiation. These phenotype-driven studies will be complemented by genomewide analyses of chromatin binding of CSL and BEN-solo factors in flies and mice, from which we will extract Notch-regulated enhancers. We will validate enhancers in vivo with emphasis on neural regulatory elements. We hope to determine conserved features of N/CSL/BEN target networks in the nervous system. In addition, these data potentially shed light on CSL-independent association of BEN-solo proteins with chromatin, which we will address using functional assays. Overall, this proposal combines a variety of experimental approaches and model systems to investigate a novel conserved neural corepressor in the Notch pathway.